retroreflective film containing a polymeric face film and method of manufacture therefore

ABSTRACT

In one aspect, there is provided a retroreflective film, comprising a retroreflective sub-structure, and a transparent polymeric film, having a surface roughness profile where the Arithmetic Mean Deviation of the Roughness Profile (Ra) ranges from about 0.18 microns to about 1.30 microns and where the Mean Spacing of Local Peaks (R—S) in the printing direction ranges from about 10 microns to about 85 microns, located over and coupled to the retroreflective sub-structure.

CROSS-REFERENCE TO RELATED APPLICATION

This Application claims the benefit of U.S. Provisional Application Ser.No. 61/039,877 filed on Mar. 27, 2008, entitled “AN IMPROVED REFLECTIVEFILM CONTAINING A POLYMERIC FACE FILM AND METHOD OF MANUFACTURETHEREFORE,” commonly assigned with the present invention andincorporated herein by reference.

TECHNICAL FIELD

The invention is directed to an improved retroreflective film and amethod of manufacturing that film.

BACKGROUND

Vehicle number plates (i.e. license plates) are commonly made to beretroreflective in order to enhance the visibility of the number plateat night.

Certain methods of fabricating retroreflective number plates commonlyinvolve the lamination of a thin retroreflective film (also commonlyreferred to as a retroreflective sheeting) to the back-side of a thick,clear plastic plate. The lamination of the retroreflective film to theclear plastic plate is often achieved with an optically clearpressure-sensitive adhesive. The clear plastic plate is commonly madefrom either acrylic or polycarbonate resin and is typically about 0.125inches thick.

When retroreflective number plates are used for the purposes of vehicleregistration, the number plates applied to each individual vehicle mustcontain a unique set of alphanumeric characters or other characters orsymbols. These characters are printed (or otherwise created) on eitherthe back surface of the plastic plate or on the top surface of theretroreflective film prior to laminating the retroreflective film to theplastic plate. The most common method currently employed to print thesecharacters is to use a computer-controlled printer such as a thermaltransfer printer, an ink jet printer, or a laser printer to print thecharacters on the front-surface of the retroreflective sheeting.

The retroreflective film employed to fabricate a number plate caninclude any of commonly known retroreflective sheeting constructions andcan incorporate any of the commonly known retroreflective elementsincluding glass microspheres or microprisms. The three most commonretroreflective sheeting constructions include enclosed lensretroreflective sheeting (incorporating the glass microspheres),encapsulated lens retroreflective sheeting (also incorporating glassmicrospheres) and microprismatic retroreflective sheeting. U.S. Pat.Nos. 2,407,680 and 4,367,920 provide detailed descriptions of the designand manufacture of enclosed lens sheeting and are incorporated herein byreference. Also, U.S. Pat. Nos. 3,109,178 and 4,025,159 provide detaileddescriptions of encapsulated lens sheeting, and U.S. Pat. Nos. 3,689,346and 4,588,258 provide descriptions of microprismatic sheeting, which areincorporated herein by reference.

Not all retroreflective sheeting materials, however, can be successfullyprinted through thermal transfer printers or other printers. To beacceptable for use in the fabrication of numbered plates, a high printquality is required. Generally, the print quality is judged acrossseveral different criteria. First, the coverage of the print must becomplete without any signs of pin-holes or other print voids, and thedepth of coverage should be full enough to provide a deep, fullysaturated print. When printing opaque colors such as black, the surfaceof the retroreflective sheeting should not show through the print.Second, the edges of printed alphanumeric characters must be straight,clean and sharp. Corners should be square. Print edges that are wavy orundefined are generally not acceptable. Third, the printed surfaceshould be uniform without any smudging or smearing. This smearing orsmudging effect is especially common with thermal transfer printing whenprinting letters such as “E”, “F”, “H”, or “T” from left-to-right wherethere exists a long horizontal bar of printing.

Certain conventional methods have attempted to overcome these printingchallenges by creating a matte surface on the face of the enclosed lenssheeting during conventional manufacturing processes. Though theseconventional approaches have allowed for an improved print quality, theydo not always provide consistent print results, and there is asignificant potential for scrap using this method of manufacturing.Moreover, the most pronounced problem with this approach is the presenceof pin-holes or printing voids when thermal transfer printing on thesurface of the enclosed lens sheeting. These defects are often caused bysurface imperfections in the top-coat of the retroreflective film,including air-bubbles, surface pits, pin-holes, and similar coatingdefects.

SUMMARY

One embodiment of this disclosure provides a retroreflective filmcomprising a retroreflective sub-structure and a transparent polymericfilm, having a surface roughness profile where the Arithmetic MeanDeviation of the Roughness Profile (Ra) ranges from about 0.18 micronsto about 1.30 microns and where the Mean Spacing of Local Peaks (R—S) inthe print direction ranges from about 10 microns to about 85 microns,located over and coupled to the retroreflective sub-structure.

Another embodiment provides a method of fabricating a retroreflectivefilm. This method embodiment comprises providing a retroreflectivesub-structure and coupling a transparent polymeric film over theretroreflective sub-structure having a surface roughness profile wherethe Arithmetic Mean Deviation of the Roughness Profile (Ra) ranges fromabout 0.18 microns to about 1.30 microns and where the Mean Spacing ofLocal Peaks (R—S) in the print direction ranges from about 10 microns toabout 85 microns.

In another embodiment, another retroreflective film is provided. Thisembodiment comprises a backing film, a first adhesive layer located overthe backing film, and an enclosed lens retroreflective film located overthe first adhesive layer. The embodiment further comprises a transparentpolymeric film, having a surface roughness profile where the ArithmeticMean Deviation of the Roughness Profile (Ra) ranges from about 0.18microns to about 1.30 microns and where the Mean Spacing of Local Peaks(R—S) in the printing direction ranges from about 10 microns to about 85microns, located over and coupled to the enclosed lens retroreflectivefilm.

In still another embodiment, another retroreflective film is provided.This embodiment comprises a backing film, a first adhesive layer locatedover the backing film, and a micro-prismatic retroreflective filmlocated over the first adhesive layer. The embodiment further comprisesa transparent polymeric film, having a surface roughness profile wherethe Arithmetic Mean Deviation of the Roughness Profile (Ra) ranges fromabout 0.18 microns to about 1.30 microns and where the Mean Spacing ofLocal Peaks (R—S) in the printing direction ranges from about 10 micronsto about 85 microns, located over and coupled to the microprismaticretroreflective film.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference is nowmade to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIGS. 1A-1C illustrate different embodiments of the invention;

FIGS. 2A-2B contrast surface roughness profiles of two different samplesmeasured in the printing direction, wherein 2A illustrates the surfaceroughness profile of an embodiment of the present invention; and

FIGS. 3A-3C illustrate additional embodiments of the invention.

DETAILED DESCRIPTION OF CERTAIN ASPECTS AND EMBODIMENTS

Certain embodiments set forth herein describe an alternativeretroreflective film construction to produce an appropriate printingsurface on the face of the retroreflective sheeting that is capable ofproducing high quality prints through thermal transfer printing or otherprint methodologies. This retroreflective film can be successfully usedin the fabrication of retroreflective number plates or other signs thatrequire a high quality print of lettering or images.

In one aspect of the invention, a polymeric face film is used as anouter-layer of the retroreflective film where the polymeric face filmpossesses a proper surface roughness profile to allow for high qualityprinting and where the polymeric face film is produced from an extrusionmanufacturing process. FIG. 1A depicts one embodiment of the newretroreflective film construction where the polymeric face film is theface film of an enclosed lens retroreflective sheeting construction.

As shown in FIG. 1A, retroreflective film 20 contains a polymeric facefilm 21. The polymeric face film 21 has an outer surface 21 a and aninner-surface 21 b. In one application, the outer surface 21 a containsa surface texture with the proper surface roughness profile to allow forsuccessful printing during the fabrication of retroreflective numberplates. After the alphanumeric characters of the number plate areprinted on the outer surface 21 a, the film 20 can be adhesivelylaminated to a clear plastic plate.

There are several different methods to incorporate polymeric face film21 into the construction of retroreflective film 20. As shown in FIG.1A, polymeric face film 21 can be laminated to a retroreflectivesub-structure 30 through the use of an optically clear laminatingadhesive 22. The retroreflective sub-structure 30 can in its own rightbe considered a very thin gauge version of an enclosed lensretroreflective sheeting as it contains its own top-coat layer 31, glassmicrospheres 32, spacing layer 33, metalized reflecting coating layer34, adhesive layer 35, and backing film layer 36. To manufacture theretroreflective film 20 depicted in FIG. 1A, the retroreflectivesub-structure 30 is first manufactured according to typicalmanufacturing techniques for enclosed lens sheeting. Then, afterremoving any temporary carrier films used during the manufacture of theretroreflective sub-structure 30, the polymeric face film 21 can beadhesive laminated to the face 30 a of the retroreflective sub-structure30.

It may also be preferable to include an optional bead bond layer 39between top-coat 31 and the glass microspheres 32 in the retroreflectivesub-structure, as seen in FIG. 1B.

Alternatively, as shown in FIG. 1C, the polymeric face film 21 can bedirectly bonded to the retroreflective sub-structure 30 without the useof a laminating adhesive. To manufacture this construction, thepolymeric face film 21 will replace the use of any temporary carrierfilms, and the top-coat 31 can be directly coated onto the inner surface21 b of the polymeric face film 21.

It is beneficial for the surface 21 a of the polymeric face film 21, andtherefore the surface of the retroreflective sheeting 20, to have theproper surface roughness profile to ensure that high quality prints canbe achieved through thermal transfer, ink jet, and other printingmethods. For example, in certain embodiments, it may be desirable tohave a matte surface on the outer surface 21 a of the polymeric facefilm 21. However, not any matte surface will function as an acceptableprinting surface for the fabrication of the retroreflective numberplates. In fact, in some instances, two different polymeric films maygenerally have the same matte appearance and gloss level but stillresult in different print qualities. More surprisingly, these same twopolymeric films may even have the same depth of surface texture thatcreate the matte surface, but the two films may still not produce thesame printing quality.

Thus, to ensure a high quality of print on the film, the surfaceroughness profile of surface 21 a preferably has an Arithmetic MeanDeviation of the Roughness Profile (Ra) between about 0.18 microns andabout 1.30 microns, and it also preferably has a Mean Spacing of LocalPeaks (R—S) in the direction of printing ranging from about 10 micronsto about 85 microns. More preferably, the Arithmetic Mean Deviation ofthe Roughness Profile (Ra) is between about 0.18 microns and about 1.00microns and the Mean Spacing of Local Peaks (R—S) in the direction ofprinting is less than about 85 μm. Still even more preferably, theArithmetic Mean Deviation of the Roughness Profile (Ra) is between about0.25 microns and about 0.55 microns and the Mean Spacing of Local Peaks(R—S) in the direction of printing is between about 20 microns and about80 microns. In advantageous embodiments, both of these parameters areconsidered and within the specified ranges to ensure high qualityprinting.

It is generally understood that many different variables can impact theoverall quality of a print. Surrounding environmental conditions such asroom temperature or humidity can lead to undesirable printing results.Similarly, cleanliness of the printing environment is important asair-borne dust particles or other contaminants can also lead toundesirable printing results. Additionally, most printers allow the userto adjust several different operating parameters such as printing speed,printing temperature, or similar variables. Given all of these manydifferent variables, those skilled in the art will recognize that it isnot expected that any given embodiment of this invention will perfectlyprint in all possible circumstances. However, we have found that themost robust embodiment of this invention which will provide acceptableprinting results under a wide variety of printing conditions andenvironmental variables will have surface roughness profiles where theArithmetic Mean Deviation of the Roughness Profile (Ra) ranges fromabout 0.30 microns to about 0.50 microns and where the Mean Spacing ofLocal Peaks (R—S) in the print direction ranges from about 25 microns toabout 55 microns.

Surface roughness profiles can be measured by following the JISB0601-2001 standard utilizing 5 samples for each measurement. The lengthof each sample can be 0.8 mm for an overall evaluation length of eachmeasurement of 4.0 mm. The preferred measurement traversing speed is 0.5mm/sec., and the results are preferably filtered using the Gaussianfilter standard. Mitutoyo Corporation of Kanagawa, Japan manufacturesseveral instruments capable of measuring the surface roughness profile.The Mitutoyo SurfTest SJ-301 Surface Roughness Tester is one suchinstrument.

FIGS. 2A and 2B depict the surface roughness profiles of two differentretroreflective film samples measured in the printing direction using aMitutoyo SurfTest SJ-301 Surface Roughness Tester. The y-axis in eachfigure represents the height and depth of various peaks and valleys asmeasured along the outer printing surface of each sample. In eachfigure, the total distance represented by the y-axis is 9 microns. Thus,the height of peak 41 in FIG. 2A is approximately 3.2 microns. Thex-axis in both Figures represents the total evaluation length of eachsample of 4.0 mm. The sample profiled in FIG. 2A is an enclosed lensretroreflective sheeting manufactured in accordance with an embodimentof the invention and contains a rigid vinyl polymeric face film havingthe proper surface roughness profile, which can be successfully printedto produce a high quality thermal transfer print. The sample producingthe profile of FIG. 2B, is also an enclosed lens retroreflectivesheeting containing a rigid vinyl polymeric face film. However, thesample of FIG. 2B does not contain the proper surface roughness profileon its outer surface to ensure a high quality print even though thesample of FIG. 2B has both a matte appearance very similar to that ofthe sample producing the profile in FIG. 2A and an Ra value within thedesired range. When printed on a thermal transfer printer, the sample ofFIG. 2B produces a high degree of smudging and smearing, particularlywhen printing letters such as “E”, “F”, “H” or “T” from left-to-right,where there exists a long horizontal line of printing.

The difference between the two samples is the Mean Spacing of LocalPeaks (R—S) as measured in the direction of printing. The sampleprofiled in FIG. 2A has a Ra value of about 0.38 microns and an R—Smeasurement in the printing direction of about 32 microns. In contrast,the sample profiled in FIG. 2B has a Ra value of about 0.55 microns andan R—S measurement in the printing direction of about 92 microns. Eventhough both Ra values are in the acceptable range, the sample with theprofile of FIG. 2B does not consistently print properly. Without beingbound by any particular theory, it is believed that the greaterfrequency of roughness peaks in the printing directions gives the samplea greater opportunity to “breathe” during printing. Therefore, it doesnot cause an excess amount of heat to be generated during the printingprocess that which could lead to one or more printing defects, includingsmudging, smearing, or poor edge quality.

It is also important to maintain the Arithmetic Mean Deviation of theRoughness Profile (Ra) within the desired range. If the Ra is too low,an excessive amount of smudging or smearing may result. If the Ra is toohigh, the depth of print may be too light resulting in either incompleteprint coverage or the ability to see the surface of the retroreflectivesheeting through the print. The latter is especially problematic whenthe printing black characters on a retroreflective sheeting that is acolor such as yellow. Another potential issue with a high Ra is that theretroreflective sheeting may not properly laminate to the under-side ofthe protective plastic plate. Tiny air bubbles may become trappedbetween the surface of the retroreflective sheeting and the adhesive. Ifthis occurs, these air bubbles will act to scatter incoming light and,thus, reduce the levels of retroreflection.

In certain advantageous embodiments, the polymeric face film is producedthrough an extrusion manufacturing process. As used herein, the phrase“extrusion manufacturing process” refers to any manufacturing process inwhich a thermoplastic resin is heated above its glass-transitiontemperature (in other words essentially melted) and then forced through(i.e. extruded through) an orifice or other opening. This includes filmextrusion where the orifice is a narrow die which forms the width andgauge of the film. It also includes film calendaring where the heatedthermoplastic resin is passed through a series of polishing rollersafter exiting the extrusion orifice to provide the film width and gauge.It further includes blown film manufacturing and other filmmanufacturing processes. Given the teachings herein, conventionalextrusion manufacturing processes may be used to form the film, such asthose that can be found in “Plastics: Materials and Processing”, by A.Brent Strong, Chapter 10, 1996, which is incorporated herein byreference.

The desired surface roughness profile can be imparted on the surface 21a of the polymeric face film 21 (FIG. 1A) either by passing the filmacross a textured roller as it is being cooled or by embossing thetexture into the film during a secondary manufacturing step. Theadvantage of using a film produced by extrusion manufacturing processescompared to liquid coating is that no matting agents are required toproduce the surface roughness profile. Further, there are no residualsolvents (or other liquids) remaining in the final film. As such, thepotential for pin-holes, bubbles, or other surface imperfections whichcould cause printing defects as discussed above is eliminated. Thus, avery consistent surface roughness profile can be created on the surfaceof the polymeric face film (and therefore on the surface of theretroreflective sheeting).

Many different polymeric resins can be utilized to produce the polymericface film 21, provided that the resin can be successfully processed intoa thin film through an extrusion manufacturing process. Further, anyresin selected must be sufficiently transparent to allow high levels ofretroreflection to be maintained in the final product construction.Examples of such polymeric resins include polyester resins, such aspolyethylene terephthalate (i.e. PET) or glycol-modified polyester (i.e.PETG); acrylic and acrylic co-polymers; polycarbonate resins;polyarylate; polyurethane resins, including polycarbonate-basedurethanes, polyester-based urethanes, and polyether-based urethanes;vinyl resins and vinyl co-polymers, such as polyvinyl chloride;ethylene-vinyl acetate copolymers; polyamide resins; polystyrene resins;polyolefin resins, such as oriented polypropylene films (i.e. OPP); andmany other resins.

The specific resin can be selected based upon considerations such asdesired durability, flexibility and stiffness, ease of handling, or costand availability. Preferred resins included vinyl resins, polycarbonateresins, acrylic resins, and polyester resins. Most preferred are vinylfilms produced from polyvinyl chloride resins. These films are moreadvantageous due to the cost-effectiveness of vinyl films and due to thegenerally favorable adhesion results of many printing inks and ribbonsto vinyl films. Such vinyl films can either be rigid or flexible (i.e.blended with plasticizers to impart flexibility and elastic propertiesto the vinyl resin). Preferred manufacturers of rigid polyvinyl chloridefilms include Omnova Solutions, Inc. of Fairlawn, Ohio, USA; KlöcknerPentaplast of America, Inc., of Gordonsville, Va., USA; and LonsealCorporation of Tokyo, Japan. Potential manufacturers of flexiblepolyvinyl chloride films include Achilles USA, Inc. of Everett, Wash.,USA.

When the enclosed lens retroreflective film 20 is utilized, the backingfilm 36 may optionally be permanently bonded to the retroreflectivesub-structure to protect the metalized reflecting coating 34. Typically,a polyester film (such as PET) may be used as the protective backingfilm with a gauge typically between about 25 μm and about 125 μm. Insome instances, it may be preferable to include a thin friction-coatingor other type of coating on the under-side of the backing film 36 toimprove handling properties or other properties. In some embodiments, apigment may be added to the adhesive 35 of the reflective substructureto provide for a better appearance on the back side of the product.

In other embodiments of the invention, the backing film may be aremovable release liner, which upon removal will expose the adhesivelayer 35 on the reverse-side of the film. In such instances, this mayallow bonding of the retroreflective film to a metal plate, sign blank,or other substrate.

Additionally, although most of the discussion has focused on enclosedlens sheeting, the polymeric face film 21 can easily be incorporatedinto other retroreflective film constructions, such as encapsulated lensretroreflective sheeting or microprismatic retroreflective sheeting asshown in FIGS. 3A and 3B and 3C. FIG. 3A depicts an encapsulated lensretroreflective film 50 where the polymeric face film 21 is functioningas the outer face film of the well-known encapsulated lens sheetingconstruction. Alternatively, the polymeric face film 21 could beadhesive laminated or otherwise bonded to a previously manufacturedencapsulated lens retroreflective sheeting. FIG. 3B depicts oneembodiment of a microprismatic retroreflective film 60 where thepolyermic face film 21 is directly bonded to a microprismaticretroreflective sub-structure 61. FIG. 3C depicts an alternativeembodiment of a microprismatic retroreflective film 70 where themicroprismatic retroreflective optical elements 72 have been vacuummetalized to form the metalized reflective coating 73. In thisembodiment, the polymeric face film 21 is bonded to the microprismaticretroreflective sub-structure 71 using an optically clear laminatingadhesive 22. Backing film 75 is bonded to the reverse side of themicroprismatic retroreflective film 70 with adhesive 74.

Additionally, other embodiments include adding UV-additives or lightstabilizers to the polymeric film 21 or to other layers to provideimproved outdoor durability. Moreover, the retroreflective film may besupplied with a printed graphic, which could be printed on either theouter-surface 21 a or inner-surface 21 b of the polymeric face film 21.Alternatively, it may be printed on the top-surface of theretroreflective sub-structure. In yet other embodiments, theretroreflective film could be supplied either as a white product (i.e.using a clear polymeric face film 21 with a clear top-coat 31 in theretroreflective sub-structure 30) or as a colored film, where atransparent pigment or dye is added to either the polymeric face film 21or the top-coat 31 or another layer of the retroreflective sub-structure30.

While most of this discussion has focused on utilizing theretroreflective film of the invention to fabricate retroreflectivenumber plates, those skilled in the art will recognize that theinvention can also be utilized to fabricate other retroreflectivearticles such as traffic signs, warning signs, construction work zonesigns, advertising or promotional signs, mailbox labels, name plates,registration plates, or any other signing article requiring a high-levelof print quality.

Different embodiments of the invention are further illustrated throughthe following examples.

EXAMPLES

Examples 1-6 were prepared by laminating a polymeric face film to anenclosed lens retroreflective sub-structure using an optically-clearlaminating adhesive. The retroreflective sub-structure contained a thinbead-bond layer between its top-coat and the glass microspheres toproduce an enclosed lens retroreflective film as illustrated in FIG. 1B.The laminating adhesive was a 25 microns thick pressure-sensitiveadhesive based upon solvent-based acrylic chemistry.

In each example, the retroreflective sub-structure contained asolvent-based acrylic top-coat, a water-based acrylic bead-bond layer,glass microspheres of 350-400 mesh size with a refractive index of 2.2,a water-based acrylic spacing layer, vacuum-deposited aluminum as themetalized reflecting coating, and a solvent-based acrylic adhesive layerbonding the backing film to the mirror coating. In all examples, thebacking film was a polyester (PET) film. The thickness of the top-coatin the retroreflective sub-structure ranged between 6 microns-50microns, and the thickness of the PET backing film was either 38microns, 50 microns, or 75 microns. All other layers were a constantthickness. By varying the thickness of these two layers, the overallgauge of the final retroreflective sheeting construction could beadjusted.

Each sample in Examples 1 through 5 was printed on either a Toshiba TECor a Taiwan Semi-Conductor Company thermal transfer printer using ablack-colored printing ribbon of 95% wax/5% resin. In Example 6, aRoland SP-300 ink jet printer was utilized. The quality of each printwas then rated as outlined below across 3 different criteria: 1) EdgeQuality; 2) Amount of Smudging and Smearing; and 3)Completeness/Coverage of Print, as set forth below.

Edge Quality:

Rating Description Very Good Edge lines are very straight and sharp.Corners are well defined. Good Slight and occasional waviness to an edgeline. Corners are still generally well defined. Moderate Some noticeablewaviness to edge lines. Corners may be slightly rounded. Poor Edge linesare fuzzy and not clearly defined. Sections of edge lines may bemissing. Corners have been cut at an angle or are very rounded.

Smudging and Smearing:

Rating Description None/Very Minor If any smearing exists, it is onlynoticeable when the sample is viewed at an angle under certain lightingconditions. Light Some smearing only along horizontal bars in letterssuch as H, E, or F, but no significant loss of edge quality in theseareas. Moderate Most visible along horizontal bars in letters such as H,E, or F with some loss in edge quality is these areas. Some slightsmearing in other areas of letters as well. Heavy Noticeable smearacross large sections of letters, often significantly impacting the edgequality near the defect. Undefined Due to incomplete print coverage, theamount of smudging or smearing could not be defined.

Print Coverage/Completeness of Print:

Rating Description Complete Full print coverage with a deep, dark print.Light Full print coverage that is generally acceptable, but print coloris not fully saturated. Very Light Full print coverage, but the printcolor is not fully saturated. Starting to see the surface of thereflective sheeting through the print. Not a generally acceptable print.Incomplete Incomplete print coverage. Can easily see the surface of thereflective sheeting through the print.

The surface roughness profile of each sample was measured using aMitutoyo SurfTest SJ-301 Surface Roughness Tester manufactured byMitutoyo Corporation of Kanagawa, Japan. The test methodology followedthat of the JIS B0601-2001 standard utilizing 5 samples for eachmeasurement. The length of each sample was 0.8 mm for an overallevaluation length of each measurement of 4.0 mm. The measurementtraversing speed was 0.5 mm/sec and the results were filtered using theGaussian filter standard. For each retroreflective sheeting sample, 4measurements were taken. Two measurements were taken in the printdirection, and two measurements were taken perpendicular to the printdirection. When reporting the Arithmetic Mean Deviation of the RoughnessProfile (Ra), all fours measurements were averaged as there were notsignificant differences between the Ra measurements in eithermeasurement direction. However, when reporting the Mean Spacing of LocalPeaks (R—S), the measurements taken in the print direction wereindependently averaged from those taken perpendicular to the printdirection.

Example 1

Example 1 demonstrates that a rigid vinyl film (i.e. polyvinyl chloridefilm), whether produced as an extruded film or a calendared film, can besuccessfully utilized as the polymeric face film in the invention. Allsamples were printed using a Taiwan Semi-Conductor Company thermaltransfer printer.

PET Backing Total Sample Sample Film Gauge Thickness ID Polymeric FaceFilm (μm) (mils) 1-A Omnova Solutions 1.7 mil Rigid 38 μm 8.1 mils VinylFilm, Frosted Matte Surface (Extruded Film)¹ 1-B Klockner 280/24 RigidVinyl 50 μm 9.8 mils Film, 3 mil Film with Dull Matte Surface(Calendared Film)² 1-C Omnova Solutions 2.0 mil Rigid 50 μm 9.2 milsVinyl Film, Dull Matte Surface (Extruded Film)¹ 1-D Klockner 280/24Rigid Vinyl 75 μm 10.7 mils  Film, 2.7 mil Film with Dull Matte Surface(Calendared Film)² 1-E Lonseal 41 μm Rigid Vinyl Film 50 μm 8.6 milswith “Normal” Gloss Surface of 40 Gloss at 60° (Calendared Film)³¹Available from Omnova Solutions, Inc. of Fairlawn, Ohio, USA ²Availablefrom Klöckner Pentaplast of America, Inc., of Gordonsville, Virginia,USA ³Available from Lonseal Corporation of Tokyo, Japan

Surface Roughness Profile R-S R-S Print Results Sample Ra (PrintDirection) (Perpendicular) Edge Smudging/ Print ID (μm) (μm) (μm)Quality Smearing Coverage 1-A 0.21 μm 35 μm   27 μm Very None/ CompleteGood Very Minor 1-B 0.37 μm 46.5 μm   37.5 μm Very Light Complete Good1-C 0.40 μm 31 μm 34.5 μm Very None/ Complete Good Very Minor 1-D 0.40μm 47 μm 41.5 μm Very None/ Complete Good Very Minor 1-E 0.47 μm 72 μm  77 μm Very None/ Complete Good Very Minor

Example 2

Example 2 demonstrates that there exists an upper limit to the depth ofsurface texture in which an acceptable print can be achieved. As shownin this example, if the Arithmetic Mean Deviation of the RoughnessProfile (Ra) is above a level of approximately 1.50 μm, the printcoverage will be too poor to provide for an acceptable print. Samples2-A and 2-B were printed using a Taiwan Semi-Conductor Company thermaltransfer printer. Sample 2-C was printed with a Toshiba TEC thermaltransfer printer.

PET Backing Total Sample Film Gauge Thickness Sample ID Polymeric FaceFilm (μm) (mils) 2-A Lonseal 4 mil Rigid Vinyl 38 μm 10.3 mils Film withEmbossed Matte Surface (Calendared Film)¹ 2-B Lonseal 45 μm Rigid VinylFilm 50 μm  8.7 mils with “Low Gloss” Matte Surface of 20 Gloss at 60°(Calendared Film)¹ 2-C Klockner 280/36 Rigid Vinyl 38 μm 13.8 mils Film,5.0 mil Film with Embossed Matte Surface (Calendared Film)² ¹Availablefrom Lonseal Corporation of Tokyo, Japan ²Available from KlöcknerPentaplast of America, Inc., of Gordonsville, Virginia, USA

Surface Roughness Profile R-S R-S Print Results Sample Ra (PrintDirection) (Perpendicular) Edge Smudging/ Print ID (μm) (μm) (μm)Quality Smearing Coverage 2-A 1.65 μm   161 μm 147.5 μm Poor UndefinedIncomplete 2-B 1.87 μm 134.5 μm   117 μm Good None/ Very Light VeryMinor 2-C 2.53 μm 185.5 μm 167.5 μm Poor Undefined Incomplete

Example 3

Example 3 demonstrates that other polymeric materials in addition torigid vinyl films can be successfully utilized as the polymeric facefilm in the invention. With respect to Sample 3-A, it is believed thatthe surface texture of the film was nearing the upper limit of anacceptable Ra value and therefore starting to cause a slightly imperfectedge. As such, because of the generally positive print results on Sample3-A, it is anticipated that lowering the Ra to below 1.00 μm, or evenmore preferably to below about 0.60 μm could further improve the qualityof edge printing and the completeness of the print coverage.

Total PET Backing Sample Sample Film Gauge Thickness ID Polymeric FaceFilm (μm) (mils) 3-A Longhua Polycarbonate PC- 38 μm 9.55 mils 813, 3mil Film with Matte Surface (Extruded Film)¹ 3-B Achilles KMC425 3.4mil/1.5 H C01 50 μm 10.4 mils Flexible Plasticized PVC Film (CalendaredFilm)² 3-C Omnova Solutions 1.1 mil 50 μm  8.2 mils PETG Co-polyesterFilm, Flat Matte Surface (Extruded Film)³ ¹Available from MianyangLonghua Film Co., Ltd. of Mianyang, Sichuan, China ²Available fromAchilles USA, Inc. of Everett, Washington, USA ³Available from OmnovaSolutions, Inc. of Fairlawn, Ohio, USA

Surface Roughness Profile R-S R-S Print Results Sample Ra (PrintDirection) (Perpendicular) Edge Smudging/ Print ID (μm) (μm) (μm)Quality Smearing Coverage 3-A 1.28 μm   53 μm 49.5 μm   Good None/ LightVery Minor 3-B 0.44 μm 64.5 μm 60 μm Very None/ Complete Good Very Minor3-C 0.38 μm 45.5 μm 39 μm Good None/ Complete Very Minor

Example 4

Example 4 demonstrates the benefits of maintaining the Mean Spacing ofLocal Peaks (R—S) in the print direction below 85 μm. A comparison ofthe print results of the samples in Example 4 with those of Example 1and Example 3 shows that the print quality can diminish with respect toboth edge definition and the amount of smudging and smearing when theR—S in the print direction is greater than 85 μm. What is particularlysurprising with Sample 4-A is that the surface appearance and depth ofsurface texture (as measured by Ra) of Sample 4-A is very similar toother samples that demonstrated positive printing results. Further, theaverage R—S value across the entire sample (i.e. averaging the R—S forthe print direction with the perpendicular direction) is approximately73, which is comparable to the R—S of other samples that yielded strongprint results (eg. Sample 1-E). However, it is believed that because theR—S as measured in the direction of printing is relatively high, a heavyamount of smearing and smudging appeared.

PET Total Backing Sample Film Gauge Thickness Sample ID Polymeric FaceFilm (μm) (mils) 4-A Klockner 254 V15 Rigid Vinyl 38 μm 11.1 mils Film,5 mil Film with Dull Matte Surface (Calendared Film)¹ 4-B Klockner280/24 Rigid Vinyl 38 μm  9.2 mils Film, 3 mil Film with Gloss SurfaceOut (Calendared Film)¹ ¹Available from Klöckner Pentaplast of America,Inc., of Gordonsville, Virginia, USA

Surface Roughness Profile R-S R-S Print Results Sample Ra (PrintDirection) (Perpendicular) Edge Smudging/ Print ID (μm) (μm) (μm)Quality Smearing Coverage 4-A 0.62 μm  90 μm 56.5 μm Good Heavy Complete4-B 0.44 μm 124 μm 54.5 μm Poor Moderate Complete

Example 5

Example 5 demonstrates that there exists a lower limit to the depth ofsurface texture in which an acceptable print can be achieved. As shownin this example, if the Arithmetic Mean Deviation of the RoughnessProfile (Ra) is below a level of approximately 0.15, smudging andsmearing may be too extensive to provide for an acceptable print.Samples 5-A and 5-B were printed using a Toshiba TEC thermal transferprinter. Sample 5-C, 5-D, and 5-E were printed with a TaiwanSemi-Conductor Company thermal transfer printer. One surprising aspectof these results is that the polymer face films of Samples 5-A, 5-B, and5-E all contain a thin coating on the outer surface in order to improveprintability. However, in all three instances, each film displayedunacceptable print quality with respect to smudging and smearing.

PET Backing Total Sample Film Gauge Thickness Sample ID Polymeric FaceFilm (μm) (mils) 5-A Innovia Films, Rayoart CGS- 50 μm 12.4 mils 360 OPPFilm with a print receptive acrylic top-coat. 3.6 mil Film. (ExtrudedFilm)¹ 5-B Exxon Mobil 50LL537, 2 mil 38 μm 10.0 mils OPP Film with aprint receptive acrylic top-coat. (Extruded Film)² 5-C LonghuaPolycarbonate PC- 38 μm 9.55 mils 813, 3 mil Film with Gloss Surface(Extruded Film)³ 5-D DR Acrylic Film, 4.6 mils, 50 μm 11.9 mils GlossSurface (Extruded Film)⁴ 5-E SKC SH82 PET Polyester Film, 50 μm  9.1mils 2 mils (Extruded Film)⁵ ¹Available from Innovia Films, Inc. ofAtlanta, Georgia, USA ²Available from Exxon Mobil Corporation ofHouston, Texas, USA ³Available from Mianyang Longhua Film Co., Ltd. ofMianyang, Sichuan, China ⁴Available from Custom Extrusion Technologiesof Lakewood, New Jersey, USA ⁵Available from SKC, Inc. of Covington,Georgia, USA

Surface Roughness Profile R-S R-S Print Results Sample Ra (PrintDirection) (Perpendicular) Edge Smudging/ Print ID (μm) (μm) (μm)Quality Smearing Coverage 5-A 0.15 μm 24.5 μm   66 μm Moderate HeavyComplete 5-B 0.11 μm   42 μm 34.5 μm Good Heavy Complete 5-C 0.10 μm30.5 μm   38 μm Good Moderate Complete 5-D 0.10 μm 16.5 μm   19 μm GoodModerate Complete 5-E  0.17 μm¹ Too Low - 21.5 Good Moderate Light NotMeasurable ¹Because of large differences between the Ra measurements inthe print direction and perpendicular direction, only the printdirection values are reported.

Example 6

Example 6 demonstrates that strong printing results can also be obtainedusing an ink jet printer instead of a thermal transfer printer. Sample6-A was prepared using the same polymeric face film as Sample 1-C. Thus,the sample had the same surface roughness profile. However, the PETbacking film gauge was 75 μm for a total sample thickness of 10.2 mils.The ink jet printer was a Roland SP-300 printer with Roland Eco-Sol Maxprinting inks. The printer settings were set for 720 DPI resolution, 1over-print, and a head pass setting of 32. Temperature settings were 36°C. for the heater and 40° for the dryer. Using these printer settings, avariety of letters in a number of different colors were printed acrossthe sample. The results are summarized in the table below.

Printing Results for Sample 6-A % of Printer Head Output Print ResultsLetter for Each CMYK Edge Smudging/ Print Printed Color Color QualitySmearing Coverage H Black 90% Black Very None/Very Complete Good Minor TBlue 1 100% Cyan, 10% Very None/Very Complete Magenta Good Minor E Blue2 100% Cyan, 20% Very None/Very Complete Magenta Good Minor F Yellow 75%Yellow, 5% Very None/Very Complete Magenta Good Minor

Example 7

Example 7 demonstrates embodiments of this invention where theretroreflective sub-structure is a microprismatic retroreflective filmas shown in FIG. 3C. To prepare Samples 7-A and 7-B, three intersectingsets of parallel V-shaped grooves were cut into a brass block using adiamond-tipped tool as outlined in U.S. Pat. No. 4,588,258 to form 42micron high forward-tilted microprisms. An electroform of thediamond-ruled brass block was then made using electrolytic deposition ofnickel on the brass block to create a mirror-image replica of it. Theelectroform was then used as a molding tool to mold microprisms into 7mil polycarbonate film. The molding was performed in a heated platenpress with temperatures between 350° F.-400° F. and pressures of about100 psi. The polycarbonate film was allowed to cool and then removed byhand from the electroform molding tool. At this point, the microprismswere present on one-side of the polycarbonate film.

After microprisms were molded, a thin layer of aluminum wasvacuum-deposited on the surface of the microprisms to form the metalizedreflective coating. This metalized microprismatic polycarbonate filmthen functioned as the body of the microprismatic retroreflectivesubstructure for both Samples 7-A and 7B. The backing film was thenlaminated to the metalized microprisms using a pressure-sensitiveadhesive to complete the formation of the microprismatic retroreflectivesubstructure as shown in FIG. 3C. As outlined in the table below, thebacking film of Sample 7-A was a removable release liner. The backingfilm of Sample 7-B was a polyester film permanently bonded to thereverse side of the sample. For each sample, the polymeric face film waslaminated to the upper-surface of the polycarbonate film using atransparent pressure-sensitive adhesive transfer tape. The table belowidentifies the materials used for the transparent polymeric face filmand for the laminating adhesive used to bond the polymeric face film tothe polycarbonate.

Constructions of Samples 7-A and 7-B Sample 7-A Sample 7-B PolymericFace Film Klockner 280/24 Rigid Vinyl Film, Omnova Solutions 2.7 milFilm with 2.0 mil Rigid Vinyl Dull Matte Surface Film, Dull Matte(Calendared Film)¹ Surface (Extruded Film)² Surface Roughness Profile Ra(μm) 0.37 μm   0.44 μm   R-S (Print Direction) 46 μm 43 μm (μm) R-S(Perpendicular) 39 μm 32 μm (μm) Face Film Laminating Mac-Tac F2001Mac-Tac F2001 Adhesive Transfer Adhesive³ Transfer Adhesive³ BackingFilm Loparex 29160 3 mil SKC SH-71E, 2 mil HDPE Release Liner⁴ polyesterfilm⁵ ¹Available from Klöckner Pentaplast of America, Inc., ofGordonsville, Virginia, USA ²Available from Omnova Solutions, Inc. ofFairlawn, Ohio, USA ³Available from MACtac of Stow, Ohio, USA ⁴Availablefrom Loparex, LLC of Willowbrook, Illinois, USA ⁵Available from SKC,Inc. of Covington, Georgia, USA

Those skilled in the art to which the invention relates will appreciatethat other and further additions, deletions, substitutions andmodifications may be made to the described embodiments without departingfrom the scope of the invention.

1. A retroreflective film, comprising: a retroreflective sub-structure; and a transparent polymeric film, having a surface roughness profile where the Arithmetic Mean Deviation of the Roughness Profile (Ra) ranges from about 0.18 microns to about 1.30 microns and where the Mean Spacing of Local Peaks (R—S) in the printing direction ranges from about 10 microns to about 85 microns, located over and coupled to the retroreflective sub-structure.
 2. The retroreflective film recited in claim 1, wherein the retroreflective film is an enclosed lens retroreflective sheeting.
 3. The retroreflective film recited in claim 1, wherein the retroreflective film is an encapsulated lens retroreflective sheeting.
 4. The retroreflective film recited in claim 1, wherein the retroreflective film is a microprismatic retroreflective sheeting.
 5. The retroreflective film recited in claim 1, wherein the Arithmetic Mean Deviation of the Roughness Profile (Ra) ranges from about 0.25 microns to about 0.55 microns and the Mean Spacing of Local Peaks (R—S) in the printing direction ranges from about 20 microns to about 80 microns.
 6. The retroreflective film recited in claim 1, wherein the transparent polymeric film is an extruded film.
 7. The retroreflective film of claim 1, wherein the transparent polymeric film comprises a vinyl co-polymer, polycarbonate, an acrylic or acrylic copolymer, a polyester or polyester co-polymer, or a polyolefin.
 8. The retroreflective film of claim 1, wherein the transparent polymeric film comprises polyvinyl chloride.
 9. A method for fabricating a retroreflective film, comprising: providing a retroreflective sub-structure; and coupling a transparent polymeric film over the retroreflective sub-structure having a surface roughness profile where the Arithmetic Mean Deviation of the Roughness Profile (Ra) ranges from about 0.18 microns to about 1.30 microns and where the Mean Spacing of Local Peaks (R—S) in the printing direction ranges from about 10 microns to about 85 microns.
 10. The method recited in claim 9, wherein coupling includes adhesively bonding the transparent polymeric film to the retroreflective sub-structure.
 11. The method recited in claim 9, wherein the transparent polymeric film is an extruded film.
 12. The method recited in claim 9, wherein the transparent polymeric film comprises a vinyl co-polymer, polycarbonate, an acrylic or acrylic copolymer, a polyester or polyester co-polymer, or a polyolefin.
 13. The retroreflective film of claim 9, wherein the transparent polymeric film comprises polyvinyl chloride.
 14. The method recited in claim 9, wherein providing includes providing a retroreflective sub-structure that comprises an enclosed lens, an encapsulated lens, or a microprismatic retroreflective film.
 15. The method recited in claim 9, wherein the surface roughness profile has an Arithmetic Mean Deviation of the Roughness Profile (Ra) which ranges from about 0.25 microns to about 0.55 microns and has a Mean Spacing of Local Peaks (R—S) in the printing direction which ranges from about 20 microns to about 80 microns.
 16. A retroreflective film, comprising: a backing film; a first adhesive layer located over the backing film; an enclosed lens retroreflective film located over the first adhesive layer; and a transparent polymeric film, having a surface roughness profile where the Arithmetic Mean Deviation of the Roughness Profile (Ra) ranges from about 0.18 microns to about 1.30 microns and where the Mean Spacing of Local Peaks (R—S) in the printing direction ranges from about 10 microns to about 85 microns, located over and coupled to the enclosed lens retroreflective film.
 17. The retroreflective film recited in claim 16, wherein the surface roughness profile has an Arithmetic Mean Deviation of the Roughness Profile (Ra) which ranges from about 0.25 microns to about 0.55 microns and has a Mean Spacing of Local Peaks (R—S) in the printing direction which ranges from about 20 microns to about 80 microns.
 18. The retroreflective film recited in claim 16, wherein the transparent polymeric film is an extruded film.
 19. The retroreflective film recited in claim 16, wherein the transparent polymeric film comprises a vinyl co-polymer, polycarbonate, an acrylic or acrylic copolymer, a polyester or polyester co-polymer, or a polyolefin.
 20. The retroreflective film of claim 16, wherein the transparent polymeric film comprises polyvinyl chloride.
 21. The retroreflective film recited in claim 16, wherein the surface roughness profile has an Arithmetic Mean Deviation of the Roughness Profile (Ra) which ranges from about 0.18 microns to about 1.0 microns and has a Mean Spacing of Local Peaks (R—S) in the printing direction less than 85 microns.
 22. The retroreflective film recited in claim 16, wherein the backing film is a polyester film or a release liner.
 23. A retroreflective film, comprising: a backing film; a first adhesive layer located over the backing film; a microprismatic retroreflective film located over the first adhesive layer; and a transparent polymeric film, having a surface roughness profile where the Arithmetic Mean Deviation of the Roughness Profile (Ra) ranges from about 0.18 microns to about 1.30 microns and where the Mean Spacing of Local Peaks (R—S) in the printing direction ranges from about 10 microns to about 85 microns, located over and coupled to the microprismatic retroreflective film.
 24. The retroreflective film recited in claim 23, wherein the surface roughness profile has an Arithmetic Mean Deviation of the Roughness Profile (Ra) which ranges from about 0.25 microns to about 0.55 microns and has a Mean Spacing of Local Peaks (R—S) in the printing direction which ranges from about 20 microns to about 80 microns.
 25. The retroreflective film recited in claim 23, wherein the transparent polymeric film is an extruded film.
 26. The retroreflective film recited in claim 23, wherein the transparent polymeric film comprises a vinyl co-polymer, polycarbonate, an acrylic or acrylic copolymer, a polyester or polyester co-polymer, or a polyolefin.
 27. The retroreflective film of claim 23, wherein the transparent polymeric film comprises polyvinyl chloride.
 28. The retroreflective film recited in claim 23, wherein the surface roughness profile has an Arithmetic Mean Deviation of the Roughness Profile (Ra) which ranges from about 0.18 microns to about 1.0 microns and has a Mean Spacing of Local Peaks (R—S) in the printing direction less than 85 microns.
 29. The retroreflective film recited in claim 23, wherein the backing film is a polyester film or a release liner. 